The present invention relates to a novel color filter and, in particular, to a novel color filter useful in the visible light range. The present invention also relates to a method for preparing the color filter.
Filters are optical lenses which are light reflective, anti-reflective, or light transmissive. They are sometimes named as reflectors, anti-reflectors, lenses, etc. according to the different purposes for which they are used (the light portions not transmitted are the portions that are reflected or absorbed, so the reflectors and the lenses function on substantially the same principle but are used for different purposes) and thus generally referred to as filters.
Filters are widely used in a variety of fields. For example, color televisions, color monitors, color decorative lamps, color image readers, as well as various optical instruments involving colors all use filters. In general, there are two types of filters: filters having a substrate (such as a transparent substrate, e.g. glass or plastics) to which an additive is added such that the lens itself provides a filtering effect, and filters having a substrate coated with films which contain one single layer or multiple layers and referred to as coated optical films, such that when light passes through the films, required reflection, interference, filtration or absorption will be resulted to achieve the desired filtering effect. The film having more than two layers is called a multilayer film. The present invention relates to the application of the latter type of filters.
As for the coated type of color filters, the materials used are closely related with the methods for preparing the filters. That is, the use of materials is restricted for different preparation methods, and the properties of the filters are affected by different materials.
Conventional methods for preparing coated filters include electron-beam gun evaporation, sputtering, and thermal evaporation processes. The materials used in these processes comprise oxides (such as silicon oxide), metal oxides (such as titanium oxide, aluminum oxide, etc.), and metals (such as aluminum, manganese, tungsten, magnesium). U.S. Pat. No. 4,887,886 discloses a filter having a single coating layer comprising silicon oxide and silicon carbide in a composite state, or silicon oxide and silicon nitride in a composite state. In that patent, the coating film is formed by vapor deposition, sputtering or ion plating. U.S. Pat. No. 4,865,405 discloses an optical filter with two multilayer films, wherein the materials for the films are not amorphous and include titanium oxide, zinc sulfide, aluminium oxide, magnesium fluoride, etc. and wherein the method for preparing the coating films is a conventional method, such as electron-beam gun evaporation. However, there are several disadvantages in association with the processes and materials disclosed in the prior art. For example, a longer time for preparation is required; when the composition of films is changed, further formulation is necessary and is extremely inconvenient; and the prepared filters provide a poor resistance to environmental changes, such as changes in temperature and humidity.